1. Field of the Invention
This invention relates to improvements in a soft focus lens for a camera capable of changing over between soft focus and normal focus or between degrees of soft focus.
2. Description of the Related Art
There are known soft focus lenses in which one of the constituent lenses is axially moved to intentionally produce spherical-aberration in the image when a soft focus effect is desired. The conventional soft focus lens has a drawback that the focal point shifts in response to changing over between the soft focus and the normal focus or to selection of a different degree of soft focus (hereinafter referred to as "selective soft control"). For this reason. even if focusing has once been accomplished, the later performance of the selective soft control would cause the image to be taken out of sharp focus. Hence, re-adjustment of the focus is required. On attempt to solve this relies on the design of a mechanical mounting for the lens, but its size and the complexity of its structure are liable to increase. The lens system which mechanically realizes the re-adjustment of the focus is known in U.S. Pat. Nos. 4,124,276 and 4,310,221.
In recent years, by the development of the auto-focus technique, the operation of re-adjusting the focus has become relatively easy. Yet, because the depression of the release button of the camera to the first stroke must be repeated, or because as this repeated depression is followed by actuation of the auto-focus apparatus, the image sensor using a CCD or the like requires an integration time and the computer takes further time to discriminate whether the image is in focus and, if out of focus, to compute the distance by which, the focusing ring must be moved and its direction from the signal of the image sensor, and the response is caused to delayed. Another problem is that when effecting the selective soft control, the camera must be kept on hold in alignment with the same object to be photographed. The technique of re-adjusting the focus of the soft focus lens by the output of the focus detecting device is mentioned in U.S. patent application Ser. No. 926,648 now U.S. Pat. No. 4,826,301 (Japanese Laid-Open Patent Applications Nos. Sho 62-112114, 62-124515 and 62-205308.
Incidentally, though not being relevant to the soft focus effect, the technique wherein the movement of one lens component is compensated by moving another lens component is mentioned in, for example, U.S. Pat. No. 4,043,642.